1. Area of the Art
The present application relates to systems for the handling and local transport of disc shaped flat sheets of stiff but flexible materials such as integrated circuit wafers, flat screen displays, glass reticules used in semiconductor chip manufacture and the like materials. Particularly, the present invention relates to an intelligent integrated circuit wafer location and handling system and a method for selectively positioning and processing both sides of a subject wafer.
2. Description of the Prior Art
Semiconductor wafers are produced by complex multi-step processes. Sophisticated integrated circuit type electronic chips are derived from wafers during processes involving often greater than 100 steps. Many of steps require extremely accurate positioning of the chips because the submicron range technologies used in manufacturing the chips are both error and inspection intensive. Also, the wafers before processing are extremely expensive, and become even more valuable after processing. There is therefore a strong need for heightened control of processing and handling methods for the involved wafers.
It follows that the high production rates required for production of integrated circuits necessitate that the wafers upon which individual circuits are located be processed rapidly and in batches. Typical wafers being processed have diameters ranging from about 4 inches to about 12 inches. Such wafers are generally housed for processing in cassettes, or caddies in closely stacked vertical arrangements.
Processing generally entails separate removal of each subject wafer from its housing cassette and loading of the same into the processing equipment utilized, followed by return of the processed wafer to a cassette or carrier. The receiving cassette may be different than the first cassette, and the fragile nature of the wafers, generally silicon, provides further constraints. Removal, processing and repositioning of these varying sized wafers has created a longstanding need for more efficient apparatus and methods for processing them. Further, because the wafers are thin as well as formed from brittle materials, the pressure exerted on the wafers by the handling device can be critical and the gripping pressure must be carefully controlled to minimize bending, cracking or chipping of the costly wafers while still assuring a firm grip on the wafer to avoid dropping it during handling.
Patented Apr. 14, 1992, the WAFER INSPECTION SYSTEM of U.S. Pat. No. 5,105,147 (xe2x80x9cKarasikovxe2x80x9d et al.) is typical of the state of at least one aspect of the existing art. The disclosed system is for the semiautomatic inspection of printed circuits on silicon wafers. Included in the Karasikov patent are the combination of a floating table, and a robotic arm optical inspection device which includes a sophisticated optoscanner for the alignment and positioning of a wafer.
Karasikov removes involved wafers by applying a vacuum to a narrow zone at the circumference of a wafer. The mechanism of the Karasikov patent highlights problems, which result in many of the processing errors ameliorated by the teachings of the present invention.
Likewise, U.S. Pat. No. 5,504,345 (xe2x80x9cBartunekxe2x80x9d et al.) which issued Apr. 2, 1996, disclosed a dual beam sensor and edge detection system and method. Two light sources, or solid state lasers, are used to detect the edges of the involved wafers. The Bartunek patent essentially shows that lasers may be used for the detection of, for example, the reflective surface of a wafer or optical disc.
Other known systems for wafer handling similarly either address improvements in locating wafers or quasi-automated means for handling wafers. It would be highly advantageous to have the capability for concurrently improving the performance of both of these functions within a single system. Capitalizing upon the use of lasers without the drawbacks of vacuum-based technology would solve many longstanding needs.
By way of example, current technology often uses a vacuum chuck mounted on a robotic arm to remove or replace individual wafers in the cassettes. Since the position of each cassette and each wafer within the cassettes is unique, the location of each disk within the three ordinal planes (xe2x80x9cX, Y, and Zxe2x80x9d) relative to some reference has to be entered into the software driving system controlling the robotics that handle the wafers.
Existing methodology requires mechanical measurement of each location followed by the data being manually entered into the software being utilized. This is a time consuming process additionally constrained by the high likelihood of human error. Sufficient differences exist among known cassettes and cassette holders, that a calibration of every cassette to be employed is generally required.
Further, these constraints are complicated by the fact that, for example, in semi-portable processing systems, relocation of any part of the system requires new calibration.
Conventional vacuum chucks, or pickup devices, referred to as vacuum end effectors, further induce harmful artifacts of the processing steps and these artifacts can result in lower industrial efficacy. Any warpage in the employed vacuum pickups may cause malfunctioring because of air leaks. Since the vacuum pickups must be thin and contain air passages, they are difficult and expensive to build. Further, since the wafer is held by the surface, the wafer is prone to slip under the high acceleration rates necessary in high speed processing. Any misalignment of the disk with the end effector can cause the system to crash. Contamination of the surface by the vacuum pickup parts on the end effector itself occurs with alarming frequency.
Likewise, a clear need exists for a way to process both sides of a semiconductor wafer. Among the prior art, various attempts at solutions to related problems, and methods for handling wafers for processing are illustrative of the paucity of patents actually addressing the above enumerated constraints. The state of the art clearly shows a need for improvement, such as taught by the present invention.
Another method of lifting wafers is the use of mechanical grippers, U.S. Pat. No. 5,570,920 (xe2x80x9cCrismanxe2x80x9d et al.) issued Nov. 5, 1996, utilizes a DC motor to drive a robotic finger. Unlike the teachings of the present invention, strain gauges 171, 173, 175 on the inner surfaces of the fingers are used to sense gripping pressure and, once an over pressure is sensed, stop the motor.
By way of further example, U.S. Pat. No. 5,435,133, which issued Jun. 13, 1995 (xe2x80x9cYasuharaxe2x80x9d et al.) utilizes servo motors which drive robotic fingers based on positioning signals. However, no sensors to indicate or control grasping force were found. Likewise, the complex attaching/detaching portion of the hand portion was the focus of Yasuhara""s disclosure, differentiating this patent from the teachings of the present invention.
Additionally, U.S. Pat. No. 5,378,033 (xe2x80x9cGuoxe2x80x9d et al.), which issued Jan. 3, 1995, utilizes a single drive mechanism for all of the involved mechanical fingers so that they apply a uniform force on the object grasped. The Guo patent teaches a purely mechanical robotic or prosthetic hand. However, the method of controlling the drive mechanism was not apparent, differentiating the Guo patent from the teachings of the present invention.
U.S. Pat. No. 5,280,981 (xe2x80x9cSchulzxe2x80x9d) issued Jan. 25, 1994 uses a load responsive two-speed drive assembly and a slip clutch (Col 9, line 63-col 10, line 28). Notably, the digit actuation mechanism of the Schulz patent contemplates neither using solenoids, voice coils nor other current generation means wherein a force directly proportional to current is used.
U.S. Pat. No. 5,188,501 (xe2x80x9cTomitaxe2x80x9d et al.) issued Feb. 23, 1992, was directed to a wafer transfer system which uses a set of claws which pivot under a wafer to serve as a lifting platform for the wafer. The Tomita patent is thus different from the teachings of the present invention because it works by creating a lifting force which cradles the wafer rather than applying a grasping force.
Issued Dec. 22, 1992, the xe2x80x9cJacobsenxe2x80x9d U.S. Pat. No. 5,172,951 does not appear to disclose a tension sensing or controlling technique. This ROBOTIC GRASPING APPARATUS operates with three degree of freedom, yet does not disclose wafer-friendly usages such as those which are an object of the present invention.
U.S. Pat. No. 5,108,140 (xe2x80x9cBartholetxe2x80x9d) issued Apr. 4, 1992, includes a palm plate and grippers having tactile or other sensors on its upper surface to detect the position of the payload or to provide input to the control mechanism (Col 5. lines 20-37).
A parallel vise like grip is generated but no means of detecting or controlling the gripping force appears to be given.
Likewise, the xe2x80x9cUlrichxe2x80x9d U.S. Pat. No. 5,501,49 (issued Mar. 26, 1996) and U.S. Pat. No. 4,957,320 (issued Sep. 18 1990) each use tactile sensors 200, 210 located on the palmar surfaces of the fingers and the palm.
U.S. Pat. No. 4,354,553 (xe2x80x9cRovettaxe2x80x9d et al.) issued Sep. 28, 1982 shows a three finger grasping system where the force applied by the fingers is supplied by traction cables 42, 43, 44 along the inner surface of the fingers such that tension applied to the fingers causes the fingers to pivot inward, tightening the grasp on the held object. Sensors 84, 85, 86, shown in FIG. 6 of the Rovetta patent, attached to the tension cables sense the traction force applied thereto, differentiating the Rovetta patent from the teachings of the present invention.
U.S. Pat. No. 4,654,793 (xe2x80x9cGuinotxe2x80x9d) also incorporates strain gauges 26, 28 on the fingers.
U.S. Pat. No. 6,092,971 to Balg et al is direceted to a system for removing wafers from a carrier using a robotic arm. This system uses a combination of a holding rake, several gripping heads which swivel and a counter holder, all of which must be used to grasp and remove the wafers.
Accordingly, since nothing among the prior art has adequately addressed the longstanding needs ameliorated by the present invention, an intelligent integrated circuit wafer handling system is offered to meet these needs.
Accordingly, it is an objective of the present invention to provide a system which overcomes the drawbacks of the prior art for chip holding apparatus and techniques. It is a farther objective to prove fail-safe means should power feed to the holding device be interrupted. It is a still further objective to provide fail safe means, which do not adversely effect the grasping sensitivity of the grasping fingers and posts during normal operation.
Briefly stated, there is provided a system for handling stiff but flexible discs, particularly semiconductor wafers, which is capable of allowing processing on both sides of a wafer. Optical beams can be employed to detect a wafer""s edge and ascertain a wafer position. Grasping by a unique robotic wafer hand assembly 101 plugged into other robotic systems for positioning is taught. A stiff wafer hand assembly member has one or more actuating rods disposed either centrally or spaced apart along the length of the member. As the wafer hand assembly member is slipped under a wafer, or between parallel stacked, spaced wafers, one or more rotating fingers, which begin in a released position are rotated 90 degrees and spaced from the wafer edge. A translator solenoid, voice coil, or combination thereof acting through an arm, applies lateral movement to the finger or a separate post to grasp the wafer. A rotator solenoid or coil 109 turns the finger 90xc2x0. This combination presents a thin profile so the wafer hand assembly member can be inserted under a top wafer between stacked, spaced wafers in a tray as shown in FIG. 8, or rotated 180xc2x0 to pick up the wafer residing in a processing device. Once positioned under, over or along side a wafer, the finger is rotated to the vertical position by the rotator solenoid. Depending on the embodiment, the finger is pulled or the post is pushed in by the translator solenoid, grasping the wafer with controlled traction force between the post(s) and the movable finger(s). Methods for use of the apparatus of the system of the present invention are also taught.
A further improvement is the addition of fail safe systems. The disks handled by the disk handling systems are fragile and if dropped can readily chip or crack. In prior available vacuum, pneumatic and electrical systems, a major drawback has been a loss or reduction of the gripping action if power to the gripper control is interrupted due to a power failure or fluctuations in the electrical control circuit. This deficiency has been eliminated in the presently described devices by adding a closing spring specifically selected to have a force, either in expansion or compression, to positively grip the disk held by the handling system if the electricity, or other force supplying means, inadvertently decreases below the force necessary to adequately hold the disc. At the same time, the spring is selected so that, should there be a total failure of the force holding the disks, the force now applied solely by the spring is such that the disks will not be damaged by the gripping means. Also included are sensing means to indicate the position of the finger and whether a disk is held in the gripper. As shown schematically in FIG. 8, the wafers are usually carried in a tray. In various different embodiments of the tray 150, the circular wafer may contact and rest on the tray sides and/or the tray bottom. More specifically, the lower most point of the wafer as it rests in the tray 150 may be in contact with a point in the center of the tray bottom (See FIG. 9).
In an alternative tray design the wafer may only contact the sides of the tray thus spacing the bottom of the wafer from the tray bottom. As a further alternative, the tray bottom may have an opening along the length thereof. If the wafer is sufficiently spaced from the bottom of the tray 150, or there is an open space in the tray bottom the wafer handling system of FIGS. 1-8, having a centrally located rotatable finger, can be used. However, if the wafer contacts the bottom of the tray 150 along the tray center line then the rotatable fingers must be spaced from the center of the front edge 124 of the handling system as shown in the embodiment of FIGS. 9-11 and more particularly in FIG. 9.
According to a feature of the present invention, there is provided a system for handling wafers and the like substrate means, which comprises, in combination, a hand assembly, a means for grasping, transporting and returning said substrate means to be handled, and at least a control means for programming and implementing a desired sequence of operations. This system may also include a separate or integral optical means for detecting a local position and orientation of a substrate means to be handled.
The system may further include optical detection means in combination with computer based identification calibration and control means for determining the size or identity of the wafers and subsequent control of the movement and positioning of the moving finger and the tension placed on the wafer grasped by the system.
According to another feature of the present invention there is provided a method for handling wafers, and related compact planar devices without damaging their surface integrity, the method comprising the steps of:
a) providing a robotic wafer hand assembly equipped with at least one or more posts, which may be fixed or moveable, a rotating finger and optical sensing means, which robotic wafer hand assembly is attached to other robotic systems for positioning;
b) reading a plurality of data regarding the relative position and orientation of a plurality of wafers;
c) grasping a wafer by use of an actuating rod disposed in a central portion of said robotic wafer;
d) locking the wafer between the post(s) and the figure(s);
e) transporting the wafer to a desired location, processing the wafer;
f) releasing said wafer into a desired location, and
g) repeating each of said steps for a subsequent wafer.
According to a feature of the present invention, there is provided a system for handling wafers and the like substrate means, which comprises, in combination, a hand assembly, an optical means for detecting a local position and orientation of a substrate means to be handled, a means for grasping, transporting and returning said substrate means to be handled, and at least a control means for programming and implementing a desired sequence of operations.
The system may further include optical detection means in combination with computer based identification calibration and control means for determining the size or identity of the wafers and subsequent control of the movement and positioning of the moving finger and the tension placed on the wafer grasped by the system.
According to another feature of the present invention there is provided a method for handling wafers, and related compact planar devices without damaging their surface integrity, the method comprising the steps of, providing a robotic wafer hand assembly equipped with at least two fixed posts, a rotating finger and optical sensing means, which robotic wafer hand assembly is attached to other robotic systems for positioning, reading a plurality of data regarding the relative position and orientation of a plurality of wafers, grasping a wafer by use of an actuating rod disposed in a central portion of said robotic wafer, locking the wafer between the fixed posts and the finger, transporting the wafer to a desired location, processing the wafer; releasing said wafer into a desired location, and repeating each of said steps for a subsequent wafer.